Electric power receiving device and non-contact power supply system

ABSTRACT

In a non-contact power supply system, an electric power receiving device with suppressed heat generation is provided. The electric power receiving device is configured with a resonance circuit which includes a resonance capacity and a resonance coil acting as a receiving antenna, and receives electric power in a non-contact manner using resonant coupling of the resonance circuit. When receiving electric power, the electric power receiving device monitors the reception electric power received by the resonance circuit and controls the resonance frequency of the resonance circuit so as to keep the reception electric power from exceeding a target electric power level (PTGT). Accordingly, even when an electric power larger than the electric power required by the electric power receiving device is transmitted from the transmitting side, the electric power receiving device operates not to receive the electric power greater than the target electric power level.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2013-138666 filed onJul. 2, 2013 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to an electric power receiving devicewhich receives electric power in a non-contact manner, and a non-contactpower supply system which includes the electric power receiving device,and relates to technology which is effective when applied to an electricpower receiving device with the use of resonant coupling of anelectromagnetic field (magnetic resonance), for example.

Practical utilization is advancing in a system using non-contact powertransmission which supplies electric power to an electrical machineryand apparatus in a non-contact manner without the intermediary of apower cord, etc. (hereinafter called a “non-contact power supplysystem”). For example, a non-contact power supply system of theelectromagnetic induction type which utilizes electromagnetic inductionbetween antennae (coils) arranged mutually spaced out, and a non-contactpower supply system of the magnetic resonance type which utilizesresonant coupling of an electromagnetic field are known.

Patent Literature 1 discloses related art technology of a non-contactpower supply system of the magnetic resonance type, for example. In thenon-contact power supply system disclosed by Patent Literature 1,electric power supplied to a primary resonance circuit which isconfigured with a coil and a capacitor on a transmitting side istransmitted to a secondary resonance circuit on a receiving side, byelectromagnetic resonant coupling. The electric power received by thesecondary resonance circuit is rectified by a rectifier circuit,converted into a DC voltage by a control circuit such as an electricpower reception IC (integrated circuit), and is utilized for electriccharging of a battery, etc.

PATENT LITERATURE

-   (Patent Literature 1) Published Japanese Unexamined Patent    Application No. 2013-21906

SUMMARY

In an electric power receiving device, such as the above-describednon-contact power supply system, which charges a battery with the use oftransmitted electric power, when the transmitted electric power isinsufficient, a sufficient amount of operation power supply will not beobtained in an electric power reception IC, and electric charging of abattery will stop. On the contrary, when the transmitted electric poweris too large, it is likely that circuit components such as an electricpower reception IC in the electric power receiving device may bedestroyed. Therefore, such a non-contact power supply system performsthe transmission control in the electric power transmitting device tooptimize the electric power to be transmitted depending on the states ofa load on the receiving side (for example, remaining amount of a batteryof the electric power receiving device). Thereby, the reliability of theelectric power transmission is enhanced. For example, when there islittle remaining amount of a battery, the electric power to betransmitted is increased, and when there is much remaining amount of abattery, the electric power to be transmitted is decreased. Through suchkinds of control, the electric power necessary for the receiving side istransmitted. However, such kinds of transmission control on thetransmitting side have a high degree of difficulty. In particular, it isdifficult to realize reliable transmission control in a non-contactpower supply system which time-shares the transmission/reception ofelectric power and the communications of information.

Accordingly, in the past, in addition to the above transmission control,by providing an over-voltage protection diode (Zener diode) coupled tothe output node of a rectifier circuit on the receiving side,comparatively larger electric power has been transmitted from thetransmitting side. According to this method, it is possible to preventoccurrence of a case where, when the load is large (for example, thereis little remaining amount of a battery), sufficient operation powersupply for the electric power reception IC is not obtained, stopping thecharging operation of a battery. Furthermore, even when the load issmall (for example, there is much remaining amount of a battery) and theelectric power transmission becomes excessive, it is possible to preventdestruction of the electric power reception IC, since the upper limit ofa voltage applied to the electric power reception IC is decided by theover-protection diode.

On the other hand, electric power receiving devices, such as amobile-phone and Smartphone, restrict a terminal's own heating value byspecifying the upper limit of consumed electric power in productspecifications. However, when an over-voltage protection diode isprovided in an electric power receiving device as described above, muchelectric power is consumed in the over-voltage protection diode at thetime of excessive electric power transmission. Therefore, it isdifficult to ignore the heating value of the over-voltage protectiondiode. In the electric power reception IC, the output voltage of arectifier circuit is stepped down to a desired target voltage with theuse of a DC-DC converter such as a series regulator or a switchingregulator. Therefore, when an over-voltage protection diode is coupledto the output node of the rectifier circuit as described above, thedifference of the output voltage of the rectifier circuit and the targetvoltage becomes large at the time of excessive electric powertransmission; therefore, the problem in the DC-DC converter is theincrease in heating value and the degradation in the conversionefficiency of electric power.

Solutions to such problems will be explained in the following. The otherissues and new features of the present invention will become clear fromthe description of the present specification and the accompanyingdrawings.

The following explains briefly an outline of typical embodiments to bedisclosed by the present application.

That is, an electric power receiving device according to the presentinvention is configured with a resonance circuit which includes aresonance capacitor and a resonance coil acting as a receiving antenna,and the electric power receiving device receives electric power in anon-contact manner with the use of resonant coupling of the resonancecircuit. The electric power receiving device, when receiving theelectric power, monitors the reception electric power received by theresonance circuit and controls a resonance frequency of the resonancecircuit so as to keep the reception electric power from exceeding atarget electric power level.

The following explains briefly an effect obtained by the typicalembodiments to be disclosed in the present application.

That is, it is possible to suppress the heat generation of the electricpower receiving device in a non-contact power supply system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing illustrating an electric power receiving deviceaccording to Embodiment 1 of the present application;

FIG. 2 is a drawing illustrating a non-contact power supply systemincluding the electric power receiving device according to Embodiment 1;

FIG. 3 is a drawing illustrating the internal configuration of aresonance circuit 130 and a resonance frequency adjustment unit 141 inthe electric power receiving device according to Embodiment 1;

FIG. 4 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 2;

FIG. 5 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 3;

FIG. 6 is a drawing illustrating characteristics of reception electricpower when a resonance frequency is changed in the electric powerreceiving device 5 according to Embodiment 3;

FIG. 7 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 4;

FIG. 8 is a drawing illustrating characteristics of reception electricpower when a resonance frequency is changed in the electric powerreceiving device 6 according to Embodiment 4;

FIG. 9 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 5;

FIG. 10 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 6;

FIG. 11 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 7;

FIG. 12 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 8;

FIG. 13 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 9;and

FIG. 14 is a drawing illustrating a non-contact power supply systemincluding an electric power receiving device according to Embodiment 10.

DETAILED DESCRIPTION 1. Outline of Embodiments

First, an outline of a typical embodiment of the invention disclosed inthe present application is explained. A numerical symbol of the drawingreferred to in parentheses in the outline explanation about the typicalembodiment only illustrates what is included in the concept of thecomponent to which the numerical symbol is attached.

<1> (An Electric Power Receiving Device which Adjusts a ResonanceFrequency so as to Keep Reception Electric Power from Exceeding aPrescribed Electric Power Level)

As illustrated in FIG. 1, the electric power receiving device (2)according to the typical embodiment of the present application isconfigured with a resonance circuit (130) which includes a resonancecapacitor (200) and a resonance coil (131) acting as a receivingantenna. The electric power receiving device (2) receives electric powerin a non-contact manner with the use of resonant coupling of theresonance circuit. The electric power receiving device, when receivingthe electric power, monitors the reception electric power received bythe resonance circuit and controls a resonance frequency of theresonance circuit so as to keep the reception electric power fromexceeding a target electric power level (PTGT).

According to this configuration, even when an electric power larger thanthe electric power required by the receiving side is transmitted fromthe transmitting side, the electric power receiving device operates notto receive the electric power greater than the target electric powerlevel.

Accordingly, the electric power receiving device does not receive theexcessive electric power more than required; therefore it is possible tosuppress the heat generation in the electric power receiving device.

<2> (Depending on the Level of the Reception Electric Power,Coincidence/Non-Coincidence of a Resonance Frequency and an ElectricPower Transmission Frequency are Controlled)

In the electric power receiving device (2) according to Paragraph 1,when the reception electric power is not exceeding the target electricpower level (PTGT), the impedance of the resonance circuit is adjustedso as to match the resonance frequency of the resonance circuit with anelectric power transmission frequency (fTx), and when the receptionelectric power is exceeding the target electric power level, theimpedance of the resonance circuit is adjusted so as to shift theresonance frequency away from the electric power transmission frequency.

With this configuration, when the electric power larger than theelectric power required by the receiving side (the target electric powerlevel) is transmitted from the transmitting side, the resonancefrequency of the receiving side departs from the electric powertransmission frequency, reducing the reception electric power of theelectric power receiving device. When the electric power smaller thanthe target electric power level is transmitted, the resonance frequencyof the receiving side approaches the electric power transmissionfrequency, increasing the reception electric power of the electric powerreceiving device. Accordingly, it is possible to easily realize thecontrol under which the electric power receiving device does not receivethe electric power more than required.

<3> (Monitoring of an Output Voltage of a Rectifier Circuit)

The electric power receiving device (2, 4-8, 11, 12) according toParagraph 1 or Paragraph 2 is configured further with a rectifiercircuit (133) which rectifies an AC voltage corresponding to theelectric power received by the resonance circuit (130, 130A-130E) andoutputs a DC output voltage, and an adjustment unit (141) which monitorsthe output voltage (VRCT) of the rectifier circuit and adjusts impedanceof the resonance circuit to keep the output voltage from exceeding atarget voltage (VTGT).

According to this configuration, it is possible to control the resonancefrequency of the resonance circuit, with ease and a high degree ofaccuracy. When the output voltage of a rectifier circuit is stepped downto a desired voltage by providing a DC-DC converter such as a seriesregulator or a switching regulator in the latter stage of the rectifiercircuit, for example, the present electric power receiving device canreduce the input-output potential difference of the DC-DC converter.Accordingly, it is possible to improve the voltage conversion efficiencyof the DC-DC converter, and to suppress the heat generation in the DC-DCconverter.

<4> (A Variable Resonance Capacitor)

In the electric power receiving device (2, 4-7, 11, 12) according toParagraph 3, the capacitance value of the resonance circuit is changedby the adjustment unit.

According to this configuration, it becomes easy to change the impedanceof the resonance circuit.

<5> (Linear Control by Means of an AMP, Adjustment of One of thePositive Side and the Negative Side of a Resonance Circuit)

In the electric power receiving device (2, 4) according to Paragraph 4,the adjustment unit includes a differential amplifier circuit (AMP)which generates a control voltage (144) so as to reduce a difference ofthe target voltage and the output voltage. The resonance circuitincludes a parallel resonance unit (202) configured with a resonancecoil (131) and a resonance capacitor (132) coupled in parallel, and afirst capacitor (CP) and a first variable resistance circuit (M1)coupled in series between one end of the parallel resonance unit and areference node (ground node) supplied with a fixed voltage. The firstvariable resistance circuit changes a value of resistance based on thecontrol voltage.

According to this configuration, by linearly controlling the resonancefrequency of the resonance circuit, it is possible to control to keepthe output voltage of the rectifier circuit from exceeding the targetvoltage. It is also possible to realize the resonance circuit which canadjust the resonance frequency, with a small number of components.

<6> (Adjustment of Both the Positive Side and the Negative Side of theResonance Circuit)

In the electric power receiving device (2) according to Paragraph 5, theresonance circuit further includes a second capacitor (CN) and a secondvariable resistance circuit (M2) coupled in series between the other endof the parallel resonance unit and the reference node. The secondvariable resistance circuit changes a value of resistance based on thecontrol voltage.

According to this configuration, a circuit for impedance adjustments,which is configured with the capacitor and the variable resistancecircuit coupled in series, is coupled to each of the positive sideterminal and the negative side terminal of the parallel resonance unit.Therefore, it is possible to maintain the symmetry of the signalwaveform of AC signals corresponding to the reception electric powergenerated at each terminal of the parallel resonance unit.

<7> (A Switching Element Configured with a Transistor)

In the electric power receiving device according to Paragraph 3 orParagraph 4, the first variable resistance circuit and the secondvariable resistance circuit are configured respectively with atransistor (M1, M2) driven by the control voltage.

According to this configuration, it is possible to realize the firstvariable resistance circuit and the second variable resistance circuitwith a simple configuration.

<8> (Switching Control by Means of a CMP)

In the electric power receiving device (5, 6) according to Paragraph 4,the adjustment unit includes a comparator circuit (150) which compares athreshold voltage (VTGT) corresponding to the target voltage and theoutput voltage, to output the comparison result (149). The resonancecircuit includes a parallel resonance unit (202) configured with theresonance coil and the resonance capacitor coupled in parallel, and afirst capacitor (CP) and a first switching element (SW1) coupled inseries between one end of the parallel resonance unit and a referencenode (ground node) supplied with a fixed voltage. The first switchingelement is on-off controlled, on the basis of the comparison result.

According to this configuration, by switching the resonance frequency ofthe resonance circuit in binary, it is possible to control to keep theoutput voltage of the rectifier circuit from exceeding the targetvoltage, and accordingly, it becomes easy to restrict the receptionelectric power of the electric power receiving device. It is alsopossible to realize the resonance circuit which can adjust the resonancefrequency, with a small number of components.

<9> (Switching Control; Adjustment of Both the Positive Side and theNegative Side of the Resonance Circuit)

In the electric power receiving device (5) according to Paragraph 8, theresonance circuit further includes a second capacitor (CN) and a secondswitching element (SW2) coupled in series between the other end of theparallel resonance unit and the reference node. The second switchingelement is on-off controlled on the basis of the comparison result.

According to this configuration, a circuit for impedance adjustments,which is configured with the capacitor and the switching element coupledin series, is coupled to each of the positive side terminal and thenegative side terminal of the parallel resonance unit. Therefore, it ispossible to maintain the symmetry of the signal waveform of AC signalscorresponding to the reception electric power generated at each terminalof the parallel resonance unit.

<10> (Coincidence and Non-Coincidence of the Resonance Frequency and theElectric Power Transmission Frequency are Controlled Depending onWhether the Target Voltage is Exceeded)

In the electric power receiving device according to Paragraph 9, theconstants of the receiving coil and the resonance capacitor of theparallel resonance unit are set up so as to match the resonancefrequency of the parallel resonance unit with the electric powertransmission frequency (fTx), when the first switching element and thesecond switching element are set to OFF. The adjustment unit sets thefirst switching element and the second switching element to ON when theoutput voltage is exceeding the target voltage and sets the firstswitching element and the second switching element to OFF when theoutput voltage is not exceeding the target voltage.

According to this configuration, it is possible to control not toreceive the electric power when the output voltage is exceeding thetarget voltage, and to receive the electric power efficiently when theoutput voltage is not exceeding the target voltage.

<11> (Plural CMPs Corresponding to Plural Threshold Voltages andCorresponding Plural Variable Capacities)

In the electric power receiving device (6) according to Paragraph 4, theadjustment unit includes plural comparator circuits (150_1-150 _(—) n)each of which compares a threshold voltage (VTGT) corresponding to thetarget voltage and the output voltage, to output the comparison result(149). The resonance circuit includes a parallel resonance unit (202)configured with the resonance coil and the resonance capacitor coupledin parallel, and plural impedance adjustment circuits configured with afirst capacitor (CN_1 (CN_2-CN_n)) and a first switching element (SW_1(SW_2-SW_n)) coupled in series between one end of the parallel resonanceunit and the reference node (ground node) supplied with a fixed voltage.Each of the plural comparator circuits has mutually different thresholdvoltage (VTGT1-VTGTn). The plural impedance adjustment circuits areprovided corresponding to the plural comparator circuits, and the firstswitching element of each of the impedance adjustment circuits is on-offcontrolled, on the basis of the comparison result of the correspondingcomparator circuit.

According to this configuration, by switching the impedance of theresonance circuit stepwise corresponding to the voltage level of theoutput voltage of the rectifier circuit, it is possible to change theresonance frequency stepwise. Therefore, it is possible to perform thecontrol of the reception state in a manner similar to the analog control(linear control). Accordingly, compared with the control in which statetransition is made between the reception enabled state and the receptiondisenabled state, it is possible to reduce an EMI noise(Electro-Magnetic Interference noise).

<12> (A Switching Element Configured with a Mechanical Switch)

In the electric power receiving device according to Paragraph 10 orParagraph 11, the first switching element and the second switchingelement are mechanical switches (SW1, SW2, SW_1-SW_n) which arecontrolled on the basis of the control voltage.

According to this configuration, parasitic capacitance of the switchingelement can be made small; accordingly, it is possible to furtheralleviate the influence on the resonance circuit according to the factthat the first capacitor and the second capacitor are coupled, when theswitching element is set to OFF.

<13> (A Variable Target Voltage)

The electric power receiving device (11) according to one of Paragraph 1through Paragraph 12 is configured further with a load circuit (139,135, BAT), and a voltage control unit (171) which receives the outputvoltage (VRCT) of the rectifier circuit and supplies it to the loadcircuit coupled in the latter stage. The voltage control unit adjuststhe target voltage so as to match the voltage to be supplied to the loadcircuit with a desired voltage.

According to this configuration, the output voltage of the rectifiercircuit is adjusted, depending on the voltage level to be supplied tothe load. Accordingly, it is possible to generate a voltage necessaryfor the load, even if a DC-DC converter such as a regulator is notprovided in the latter stage of the rectifier circuit. Therefore, if therequirement specification of the electric power receiving device issatisfied, it is possible to remove the existing DC-DC converter etc.,contributing to the reduction of the circuit scale of the electric powerreceiving device.

<14> (A Variable Resonance Capacitor by a PIN Diode)

In the electric power receiving device (7) according to Paragraph 4, theresonance circuit (130D) includes a PIN diode (DPN) to which a variablebias voltage is applied by the adjustment unit.

According to this configuration, it is possible to change easily thecapacitance value of the resonance circuit.

<15> (A Variable Resonance Coil)

In the electric power receiving device (8) according to Paragraph 3, theresonance circuit (130E) changes the inductance of the receiving coil(131).

According to this configuration, it becomes easy to change the impedanceof the resonance circuit.

<16> (Monitoring of an Input Voltage of a Rectifier Circuit)

The electric power receiving device (9, 10) according to Paragraph 3further includes a rectifier circuit (133) which rectifies an AC voltagecorresponding to the electric power received by the resonance circuit(130) and outputs a DC output voltage, and an input voltage detectionunit (160, 164) which detects the input voltage supplied to therectifier circuit via the resonance circuit. The electric powerreceiving device further includes an adjustment unit (141) which adjuststhe impedance of the resonance circuit to keep the input voltagedetected by the input voltage detection unit from exceeding a targetvoltage.

According to this configuration, it is possible to control the resonancefrequency of the resonance circuit so as not to receive an electricpower greater than the target electric power level. Since the receptionelectric power is detected in earlier stage than the rectifier circuit,it is possible to improve the responsiveness of the control system.

<17> (The Input Voltage of Both the Positive Side and the Negative Sideof the Rectifier Circuit is Detected)

In the electric power receiving device (9) according to Paragraph 16,the rectifier circuit is a full wave rectifier circuit. The inputvoltage detection unit (160) includes a first peak hold circuit (161)which detects a peak value of a positive side input voltage of therectifier circuit, and a second peak hold circuit (162) which detects apeak value of a negative side input voltage of the rectifier circuit.The input voltage detection unit further includes an averaging circuit(163) which outputs an average value of the peak value detected by thefirst peak hold circuit and the peak value detected by the second peakhold circuit. The adjustment unit adjusts the impedance of the resonancecircuit to keep the average value (VPA) of the averaging circuit fromexceeding the target voltage (VTGT).

According to this configuration, even when the voltage waveformsinputted into the positive side and the negative side of the rectifiercircuit are asymmetrical, it is possible to control the impedance of theresonance circuit with a high degree of accuracy.

<18> (A Non-Contact Power Supply System)

The non-contact power supply system (20-29) according to the typicalembodiment of the present application is configured with an electricpower transmitting device (1, 3) which transmits electric power in anon-contact manner with the use of the electromagnetic resonant couplingutilizing the resonance circuit, and the electric power receiving device(2, 4-12) according to one of Paragraph 1 through Paragraph 17 whichreceives the electric power transmitted by the electric powertransmitting device in a non-contact manner.

According to this configuration, it is possible to realize a reliablenon-contact power supply system, suppressing the complexity of thetransmission control in the electric power transmitting device.

<19> (An Electric Power Receiving Device which Controls the Impedance ofa Resonance Circuit to Match the Reception Electric Power with theTarget Electric Power)

Another electric power receiving device (2, 4-12) according to thetypical embodiment of the present application includes a resonancecircuit (130, 130A-130E) configured with a resonance capacitor and aresonance coil acting as a receiving antenna, and receives electricpower in a non-contact manner with the use of resonant coupling of theresonance circuit. When receiving the electric power, the electric powerreceiving device according to the present invention controls dynamicallythe impedance of the resonance circuit to match the reception electricpower received by the resonance circuit with a target electric powerlevel (PTGT).

According to this configuration, even when an electric power larger thanthe electric power required by the receiving side is transmitted fromthe transmitting side, the electric power receiving device operates soas to match the reception electric power with the target electric powerlevel.

Accordingly, the electric power receiving device does not receive theexcessive electric power more than required; therefore, it is possibleto suppress the heat generation in the electric power receiving device.

2. Details of Embodiments

The embodiments are further explained in full detail. In the entirediagrams for explaining the embodiments of the present invention, thesame symbol is attached to an element which possesses the same function,and the repeated explanation thereof is omitted.

Embodiment 1 The Outline of a Non-Contact Power Supply System

FIG. 2 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 1. Thenon-contact power supply system 20 illustrated in the figure includes anelectric power transmitting device 1 and an electric power receivingdevice 2. In the non-contact power supply system 20, the electric powersupply from the electric power transmitting device 1 to the electricpower receiving device 2 is possible in a non-contact manner(wirelessly). Although not restricted in particular, in the non-contactpower supply system 20, non-contact power transmission is realized bythe magnetic resonance method utilizing resonant coupling of anelectromagnetic field. In the non-contact power transmission, thefrequency fTx of an electric power transmission signal outputted as anelectric power to be transmitted (electric power transmission frequency)is a frequency in MHz zone, for example.

In the non-contact power supply system 20, transmission and reception ofdata are mutually enabled between the electric power transmitting device1 and the electric power receiving device 2, by the short distance radiocommunication. The short distance radio communication may utilize an NFC(Near Field Communication), for example (called hereinafter “NFCcommunications”). Although not restricted in particular, the electricpower receiving device 2 uses one antenna for both the non-contact powersupply of the magnetic resonance type and the NFC communications, and itis possible to switch between the electric power reception and thecommunications of information.

<A Configuration of the Electric Power Transmitting Device 1>

The electric power transmitting device 1 is configured with, forexample, an oscillator 101, a transmitting amplifier 102, a power supplycircuit (REG_CIR) 103, a control circuit (CNT_CIR) 104, a communicationunit (CMM_CIR) 105, a communication coil antenna 106, an electric powersupply coil 107, a resonance coil 108, and a resonance capacitor 109.

The oscillator 101 generates an AC signal of a frequency correspondingto an electric power transmission signal for transmitting the electricpower from the electric power transmitting device 1. Although notrestricted in particular, the frequency of the AC signal outputted fromthe oscillator 101 is fixed and equal to the frequency of the electricpower transmission signal (electric power transmission frequency) fTx.The transmitting amplifier 102 amplifies the AC signal outputted fromthe oscillator 101, and generates a driving signal corresponding to themagnitude of the electric power to be transmitted. The transmittingamplifier 102 is a variable gain amplifier of which the amplificationfactor is variable. The transmitting amplifier 102 operates at a voltagegenerated by the power supply circuit 103 as a power supply, forexample, and its amplification factor is varied by adjusting a biasvoltage and a bias current which are supplied to the transmittingamplifier 102. The power supply circuit 103 generates plural voltagesused as an operation power supply of each functional section of theelectric power transmitting device 1, on the basis of an input voltageVIN supplied from a power supply adapter, a universal serial bus (USB),etc. For example, the power supply circuit 103 generates a voltage usedas the operation power supply of the transmitting amplifier 102 asdescribed above, and a voltage used as the operation power supply of thecontrol circuit 104.

The driving signal outputted from the transmitting amplifier 102 issupplied to the electric power supply coil 107. The electric powersupply coil 107 and the resonance coil 108 are coupled magnetically, andthe AC power related to the driving signal supplied to the electricpower supply coil 107 is supplied to the resonance coil 108 byelectromagnetic induction. The resonance coil 108 and the resonancecapacitor 109 configure the resonance circuit 110 on the primary side.The resonance circuit 110 is a parallel resonant circuit where theresonance coil 108 and the resonance capacitor 109 are coupled inparallel, for example. When a magnetic field is generated by resonanceby means of the resonance circuit 110, the electric power is transmittedfrom the electric power transmitting device 1.

The communication unit 105 performs NFC communications via thecommunication coil antenna 106. For example, the NFC communicationsrealize an exchange of the authentication data for authenticatingwhether the electric power receiving device 2 is an electric powertransmission target of the electric power transmitting device 1, anexchange of the reception notice for notifying whether the electricpower receiving device 2 has received the electric power transmittedfrom the electric power transmitting device 1, and others.

The control circuit 104 includes a program execution device whichexecutes data processing according to a program stored in a memory, etc.The control circuit 104 is a micro controller, for example, and isrealized with a semiconductor device which encapsulates a semiconductorchip formed over a semiconductor substrate like one single crystalsilicon by the well-known CMOS integrated circuit manufacturingtechnology, with an insulating resin such as a mold resin. The controlcircuit 104 performs centralized control of the electric powertransmitting device 1. For example, the control circuit 104 controls theexecution and halt of the wireless communications via the communicationunit 105 and the communication coil antenna 106, and the non-contactpower transmission via the resonance coil 108. In addition, the controlcircuit 104 performs various kinds of data processing in the wirelesscommunications and various kinds of data processing related to thenon-contact power transmission. By performing the NFC communicationswith the electric power receiving device 2 via the communication coilantenna 106, the control circuit 104 performs exchange of theinformation on the remaining amount of a battery BAT in the electricpower receiving device 2 and the various kinds of information for thenon-contact power supply, and determines the electric power amount to betransmitted. Then, the control circuit 104 adjusts the amplificationfactor of the transmitting amplifier 102 according to the electric poweramount determined. Accordingly, an electric power corresponding to theelectric power amount to be transmitted is sent out from the electricpower transmitting device 2.

<A Configuration of the Electric Power Receiving Device 2>

The electric power receiving device 2 is a small portable device, suchas a mobile terminal, for example, and performs the transmission andreception of data by use of wireless communications and the electriccharging of a battery BAT, etc. by use of non-contact power supply. Asdescribed above, the electric power receiving device 2 switches betweenthe NFC communications and the electric power reception, using theresonance coil 131 as the common antenna of the antenna employed for theNFC communications, and the antenna employed for the non-contact powersupply of the electromagnetic resonance method.

The electric power receiving device 2 is configured with a resonancecoil 131, a resonance capacitor 200, a rectifier circuit (RCR_CIR) 133,an electric power reception IC 140, a control circuit (CNT_CIR) 136, acommunication unit 137, an internal electronic circuit (EC) 139, and abattery BAT, for example.

The resonance coil 131 and the resonance capacitor 200 configure asecondary resonance circuit 130, and produce electromotive force (ACsignal) by the resonant interaction of the magnetic field generated bythe primary resonance circuit 110 of the electric power transmittingdevice 1. Although the details thereof will be described later, theresonance circuit 130 is a parallel resonant circuit where a coil and acapacitor are coupled in parallel. Hereinafter, one connection node (apositive-side node) where the coil and the capacitor are coupled isexpressed by a reference symbol NDP, and the other connection node (anegative-side node) is expressed by a reference symbol NDN.

In the resonance circuit 130, the resonance frequency is changed byadjusting the impedance thereof. For example, the impedance of theresonance circuit 130 is adjusted to shift the resonance frequency ofthe resonance circuit 130 so as to coincide with an electric powertransmission frequency fTx. As the result, it is possible to receiveefficiently the magnetic field from the electric power transmittingdevice 1. Although not restricted in particular, the resonance circuit130 is configured such that the impedance of the resonance circuit 130is adjusted by changing the capacitance value of the resonance capacitor200. The internal configuration of the resonance circuit 130 isdescribed later.

The rectifier circuit 133 rectifies an AC voltage (AC signal)corresponding to the electric power received by the resonance circuit130 and obtains a DC output voltage. The rectifier circuit 133 is a fullwave rectifier circuit, for example. Although not restricted inparticular, the rectifier circuit 133 is configured with a diode bridgecircuit of Schottky diodes D1-D4, and a smoothing capacitor C3. Oneinput terminal (a connection node of the diode D1 and the diode D2) ofthe diode bridge circuit is coupled to the node NDP via a capacitor C1,and the other input terminal (a connection node of the diode D3 and thediode D4) is coupled to the node NDN via a capacitor C2. The capacitorsC1 and C2 form a matching circuit for adjusting the impedance of therectifier circuit 133 viewed from the resonance circuit 130. Thecapacitors C1 and C2 can be deleted depending on the matching state ofthe impedance.

The smoothing capacitor C3 smoothes the voltage rectified by the diodebridge circuit. The smoothing capacitor C3 is coupled between the outputnode of the diode bridge circuit and the ground node. Hereinafter, thevoltage of the diode bridge circuit at the output node thereof isexpresses as a rectified voltage VRCT.

On the basis of the rectified voltage VRCT, the operation of eachfunctional section in the electric power receiving device 2 is enabled.In FIG. 2, the electric power reception IC 140, the internal electroniccircuit 139, and the battery BAT are representatively illustrated as aload circuit 201 of the rectifier circuit 133.

The electric power reception IC 140 generates a stable DC voltage basedon the rectified voltage VRCT. At the same time, the electric powerreception IC 140 supplies the operation power of the internal electroniccircuit 139, the charge voltage to the battery BAT, the operation powerof the communication unit 137 and the control unit 136, etc. Althoughnot restricted in particular, the electric power reception IC 140 is asemiconductor device which encapsulates a semiconductor chip formed overa semiconductor substrate like one single crystal silicon, by thewell-known CMOS integrated circuit manufacturing technology, with aninsulating resin such as a mold resin.

Specifically, the electric power reception IC 140 includes a powersupply circuit (REG_CIR) 134 and a charging control circuit (CHGCNT)135. The power supply circuit 134 converts the rectified voltage VRCTinto a fixed voltage of a desired magnitude. The power supply circuit134 is a DC-DC converter, for example, and configures a step-downswitching regulator or a series regulator (LDO: Low Drop Out), etc.,with an external coil and an external stabilization capacity, etc. Thecharging control circuit 135 controls electric charging of the batteryBAT by the DC voltage generated by the power supply circuit 134. Forexample, by monitoring the charge current of the battery BAT and theterminal voltage of the battery BAT, the charging control circuit 135detects the states of the battery BAT (the full charge capacity, theremaining amount, the charging state, etc.), and controls the execution,halt, etc. of the electric charging. Although not restricted inparticular, the charging control circuit 135 is a micro controller.

The battery BAT is a secondary battery to which electric charging ispossible by the DC voltage generated by the power supply circuit 134.Although not restricted in particular, the battery BAT is a battery ofone cell (4.0-4.2V), for example, such as a lithium-ion battery. Theinternal electronic circuit 139 is an electronic circuit for realizingthe characteristic function as the electric power receiving device 2(for example, if the electric power receiving device 2 is Smartphone,the characteristic function is the function expected as Smartphone).

The communication unit 137 employs the resonance coil 131 as acommunications antenna, to perform wireless communications (NFCcommunications) with the electric power transmitting device 1.Specifically, the communication unit 137 is configured with a switchingcircuit (SEL) 1370 and a communication control circuit (CMM_CIR) 1371.According to the signal level of the AC signal corresponding to theelectric power received by the resonance circuit 130, the switchingcircuit 1370 controls whether the AC signal concerned is supplied to thecommunication control circuit 1371 or not. For example, when the signallevel of the AC signal corresponding to the electric power received bythe resonance circuit 130 exceeds a prescribed threshold, the supply ofthe AC signal to the communication control circuit 1371 is shut down,and when the signal level of the AC signal does not exceed theprescribed threshold, the AC signal is supplied to the communicationcontrol circuit 1371.

The communication control circuit 1371 is a micro controller, forexample, and performs the various kinds of control and data processingfor realizing the wireless communications via the resonance coil 131 asthe communications antenna. Although not restricted in particular, thecommunication control circuit 1371 is realized with a semiconductordevice which encapsulates a semiconductor chip formed over asemiconductor substrate like one single crystal silicon, by thewell-known CMOS integrated circuit manufacturing technology, with aninsulating resin such as a mold resin.

The control circuit 136 performs centralized control of the electricpower receiving device 2. For example, the control circuit 136 controlsthe execution and halt of the wireless communications via the resonancecoil 131, and the various kinds of data processing in the wirelesscommunications (for example, the modulation and demodulation of areceived signal). In addition, the control circuit 136 performs theoperation control (enabling control) of the power supply circuit 134 andcontrols the execution and halt of the charge control of the battery BATby means of the charging control circuit 135. Although not restricted inparticular, the control circuit 136 is a micro controller, and isrealized with a semiconductor device which encapsulates a semiconductorchip formed over a semiconductor substrate like one single crystalsilicon, by the well-known CMOS integrated circuit manufacturingtechnology, with an insulating resin such as a mold resin.

<Control of the Reception Electric Power Through Adjustment of aResonance Frequency>

As described above, the electric power transmitting device 1 sends outthe electric power to be transmitted corresponding to the electric poweramount required by the electric power receiving device 2, on the basisof the information on the remaining amount, etc. of the battery BAT inthe electric power receiving device 2. However, due to the difficulty ofthe transmission control by means of the electric power transmittingdevice 1, there is a possibility that a larger transmission electricpower than the electric power required by the electric power receivingdevice 2 is outputted. In such a case, in order that the electric powerreceiving device 2 may not receive a larger electric power thanrequired, the electric power receiving device 2 possesses a function formonitoring the reception electric power in the electric power receivingdevice 2, and for controlling the resonance frequency of the resonancecircuit so as to keep the reception electric power from exceeding anelectric power level aimed at (a target electric power level).Specifically, the electric power receiving device 2 is configuredfurther with a resonance frequency adjustment unit (FRQ_CNT) 141.

The resonance frequency adjustment unit 141 monitors the receptionelectric power received by the resonance circuit 130 and controls theresonance frequency of the resonance circuit 130 so that the receptionelectric power does not exceed the target electric power level PTGT (sothat the reception electric power coincides with the target electricpower level PTGT).

More specifically, when the reception electric power does not exceed thetarget electric power level PTGT, the resonance frequency adjustmentunit 141 adjusts the impedance of the resonance circuit 130 so as tomatch the resonance frequency of the resonance circuit 130 with theelectric power transmission frequency fTx, and when the receptionelectric power exceeds the target electric power level PTGT, theresonance frequency adjustment unit 141 adjusts the impedance of theresonance circuit 130 so as to shift the resonance frequency away fromthe electric power transmission frequency fTx. The monitoring of thereception electric power by means of the resonance frequency adjustmentunit 141 is performed by detecting a rectified voltage VRCT, forexample.

Hereinafter, the control of the resonance frequency of the resonancecircuit 130 by means of the resonance frequency adjustment unit 141 isexplained in detail.

FIG. 3 illustrates the internal configuration of the resonance circuit130 and the resonance frequency adjustment unit 141 in the electricpower receiving device according to Embodiment 1. In the figure, forconvenience of explanation, only functional blocks surrounding theresonance circuit 130 and the resonance frequency adjustment unit 141are shown, and other functional blocks are not shown. As for theelectric power transmitting device 1 in the figure, an electric powertransmitting coil 108 and a resonance capacitor 109 are shown, and otherfunctional blocks are shown in a simplified form.

As illustrated in the figure, the resonance frequency adjustment unit141 is configured with a differential amplifier circuit AMP. Thedifferential amplifier circuit AMP functions as an error amplificationcircuit which generates a control voltage 144 so as to reduce thedifference of the target voltage VTGT determined corresponding to thetarget electric power level PTGT and the output voltage VRCT of therectifier circuit 133. The target voltage VTGT is determinedcorresponding to the voltage required by the electric power reception IC140 which receives the supply of the rectified voltage VRCT, forexample. For example, even if the maximum voltage which is allowed to beapplied to the input terminal IN of the electric power reception IC 140(the withstand voltage of the electric power reception IC 140) is 25V,when the voltage necessary as the input voltage of the power supplycircuit 134 of the electric power reception IC 140 is 10V, the targetvoltage VTGT is set as 10V. Accordingly, the differential amplifiercircuit AMP generates the control voltage 144 so as to keep the outputvoltage VTGT of the rectifier circuit 133 from exceeding 10V (so as tobe equal to 10V).

Although not restricted in particular, the target voltage VTGT isgenerated by a reference voltage generating circuit (not shown) providedin the electric power receiving device 2, and is supplied to thedifferential amplifier circuit AMP. The reference voltage generatingcircuit is not restricted in particular, and it may be a regulatorcircuit provided in the power supply circuit 134 in the electric powerreception IC 140, or may be a regulator circuit provided separately fromthe power supply circuit 134.

The resonance circuit 130 is configured with a parallel resonance unit202 in which a resonance coil 131 and a resonance capacitor 132 arecoupled in parallel, and impedance adjustment circuits 142 and 143coupled between each of the terminals (nodes NDP, NDN) of the parallelresonance unit 202 and the reference node to which a fixed voltage issupplied. The resonance capacitor 132 and the impedance adjustmentcircuits 142 and 143 configure the capacitor 200 as the variablecapacity.

Although the reference node is a ground node to which the ground voltageis supplied, for example. However, if the node is fixed with respect toDC, the node is not restricted to the ground node.

The impedance adjustment circuit 142 includes a capacitor CP of whichone end is coupled to the node NDP and a variable resistance circuit1420 which is coupled between the other end of the capacitor CP and theground node. In the variable resistance circuit 1420, a value of theresistance thereof is varied by the control voltage 144 from thedifferential amplifier circuit AMP. The variable resistance circuit 1420is configured with a transistor M1, for example. Although not restrictedin particular, as the transistor M1, a field effect transistor, an IGBT,etc. having a small on-resistance and a high withstand voltage can beemployed. FIG. 3 illustrates the case where the MOS transistor having ahigh withstand voltage is employed. A source electrode of the transistorM1 is coupled to the ground node, and a drain electrode is coupled tothe capacitor CP. The control voltage 144 is supplied to a gateelectrode of the transistor M1. The circuit configuration of thevariable resistance circuit 1420 is not restricted to the oneillustrated in FIG. 3, but another circuit configuration will beapplicable, as long as the value of resistance between the capacitor CPand the ground node can be varied according to the control voltage 144.

The impedance adjustment circuit 143 also has the same configuration asthe impedance adjustment circuit 142. For example, the impedanceadjustment circuit 143 includes a capacitor CN of which one end iscoupled to the node NDN and a variable resistance circuit 1430 which iscoupled between the other end of the capacitor CN and the ground node.The variable resistance circuit 1430 is configured with a transistor M2,for example, and is driven according to the control voltage 144, as isthe case with the transistor M1.

By coupling the impedance adjustment circuits 142 and 143 to thepositive side terminal (node NDP) and the negative side terminal (nodeNDN) of the parallel resonance unit 202, respectively as describedabove, it is possible to maintain the waveform symmetry of the ACsignals (to suppress distortion of the electric power receptionwaveform) corresponding to the reception electric power generated at thenode NDP and the node NDN, respectively.

In the present embodiment, the constants of the resonance coil 131 andthe resonance capacitor 132 have been determined so as to match theresonance frequency of the parallel resonance unit 202 (the resonancefrequency determined by the resonance coil 131 and the resonancecapacitor 132) with the electric power transmission frequency fTx. Here,it is assumed that the parasitic capacitance of the transistors M1 andM2 and others can be ignored. In the present conditions, when therectified voltage VRCT becomes lower than the target voltage VTGT, thecontrol voltage 144 is controlled to become low by the differentialamplifier circuit AMP. Accordingly, the gate-to-source voltage of thetransistors M1 and M2 decreases. Therefore, the value of resistancebetween the drain and the source increases, and the influence of thecapacitors CP and CN as the capacity component in the resonance circuit130 is reduced. That is, the resonance capacitor 132 becomes dominant asthe capacity component of the resonance circuit 130, and the resonancefrequency of the resonance circuit 130 approaches the resonancefrequency determined by the resonance coil 131 and the resonancecapacitor 132; that is, the electric power transmission frequency fTx.Finally, when the transistors M1 and M2 become in OFF state, thecapacitors CP and CN become in a disconnected state, and the resonancefrequency of the resonance circuit 130 substantially coincides with theelectric power transmission frequency fTx. Therefore, when the rectifiedvoltage VRCT is lower than the target voltage VTGT, the control by thedifferential amplifier circuit AMP is performed so as to match theresonance frequency of the resonance circuit 130 with the electric powertransmission frequency fTx.

On the other hand, when the rectified voltage VRCT becomes higher thanthe target voltage VTGT, the control voltage 144 is controlled to becomehigh by the differential amplifier circuit AMP. Accordingly, thegate-to-source voltage of the transistors M1 and M2 increases.Therefore, the value of resistance between the drain and the sourcedecreases, and the influence of the capacitors CP and CN as the capacitycomponent in the resonance circuit 130 is increased. That is, theresonance frequency of the resonance circuit 130 is determined by theresonance coil 131, the resonance capacitor 132, and the capacitors CPand CN. Accordingly, the resonance frequency of the resonance circuit130 deviates from the electric power transmission frequency fTx.Therefore, when the rectified voltage VRCT is higher than the targetvoltage VTGT, the control by the differential amplifier circuit AMP isperformed so as to shift the resonance frequency of the resonancecircuit 130 away from the electric power transmission frequency fTx.

In this way, by controlling the resonance frequency of the resonancecircuit 130 linearly, the reception electric power of the electric powerreceiving device 2 is restricted so as to keep the rectified voltageVRCT from exceeding the target voltage VTGT.

As described above, according to the electric power receiving deviceaccording to Embodiment 1, the reception electric power received by theresonance circuit 130 is monitored, and the resonance frequency iscontrolled so as to keep the reception electric power from exceeding thetarget electric power level PTGT. Therefore, even when an electric powerlarger than the electric power required by the receiving side istransmitted from the transmitting side, the electric power receivingdevice 2 operates not to receive the electric power greater than thetarget electric power level. Accordingly, the electric power receivingdevice 2 does not receive the excessive electric power more thanrequired; therefore, it is possible to suppress the heat generation inthe electric power receiving device 2. For example, even when anover-voltage protection diode is coupled to the output node of therectifier circuit 133 as in the related art, the generation of heatbased on the surplus electric power consumed in the over-voltageprotection diode can be suppressed. Therefore, it is possible tosuppress the heating value of the entire electric power receivingdevice, compared with the past.

By applying the present electric power receiving device to a non-contactpower supply system, it becomes possible to realize a reliablenon-contact power supply system, suppressing that the transmissioncontrol in the electric power transmitting device becomes complicated.For example, the present electric power receiving device operates not toreceive an electric power greater than the target electric power level,even when an electric power larger than the electric power required istransmitted. Therefore, even if the reliability of the transmissioncontrol on the transmitting side is somewhat low, there is littlepossibility that the electric power receiving device may be destroyeddue to heat generation more than required. Therefore, it is possible toenhance the entire reliability of the non-contact power supply system,attaining the simplification of the internal electronic circuit for theelectric power transmission control and the program for controlling itin the electric power transmitting device.

Furthermore, as described above, the reception electric power ismonitored by monitoring the output voltage VRCT of the rectifier circuit133, and the impedance of the resonance circuit 130 is adjusted so as tokeep the output voltage VRCT from exceeding the target voltage VTGT. Bythis method, it is possible to control the resonance frequency, withease and a high degree of accuracy. Since the control is performed so asto keep the output voltage VRCT from exceeding the target voltage VTGT,it is possible to reduce the difference between the input voltage (therectified voltage VRCT) and the output voltage in the power supplycircuit 134, more than those in the past. That is, it is possible toreduce the input-output potential difference of the DC-DC converterconfigured by the power supply circuit 134. For example, in the past,when a DC-DC converter has generated an output voltage of 5V, an inputvoltage (a rectified voltage VRCT) of the DC-DC converter may have risenup to the upper limit voltage (for example, 20V) determined by anover-voltage protection diode. As compared with this, according to thepresent electric power receiving device, the input voltage of the DC-DCconverter is controlled not to exceed the target voltage VTGT (forexample, 10V). Therefore, it is possible to reduce the input-outputpotential difference of the DC-DC converter (the power supply circuit134) more than those in the past. Accordingly, it becomes possible toimprove the voltage conversion efficiency by means of the DC-DCconverter, and to suppress the heat generation in the DC-DC converter(the power supply circuit 134).

Embodiment 2

FIG. 4 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 2.

An electric power receiving device 4 in a non-contact power supplysystem 21 according to Embodiment 2 is different from the electric powerreceiving device according to Embodiment 1 in the point that animpedance adjustment circuit is coupled only to one terminal of theparallel resonance unit in the resonance circuit on the receiving side.The configuration of other parts of the electric power receiving device4 is the same as that of the electric power receiving device 2 accordingto Embodiment 1, therefore, the same symbol is attached to the samecomponent as the electric power receiving device 2, and the detailedexplanation thereof is omitted.

As illustrated in FIG. 4, the resonance circuit 130A in the electricpower receiving device 4 has a configuration in which the impedanceadjustment circuit 142 is coupled to one terminal (the node NDP) of theparallel resonance unit 202, and no impedance adjustment circuit iscoupled to the other terminal (the node NDN).

According to this configuration, as is the case with the electric powerreceiving device 2 according to Embodiment 1, it is possible not toreceive an excessive electric power more than the electric powerrequired by the electric power receiving device 4, and to suppress theheat generation of the electric power receiving device 4. According tothe electric power receiving device 4, the symmetry of AC signalscorresponding to the reception electric power generated at the node NDPand the node NDN may collapse. However, when the degree of the collapseof the symmetry is allowable, it is possible to reduce the number ofcomponents which are otherwise to be added. Therefore, it is possible tosuppress the increase in cost of the electric power receiving deviceaccompanied by enabling the adjustment of the resonance frequency.

It is sufficient that the impedance adjustment circuit for adjusting theresonance frequency is coupled to either of the positive side terminalor the negative side terminal of the parallel resonance unit 202, and itis not restricted to the configuration in which the impedance adjustmentcircuit is coupled to the positive side terminal (the node NDP) of theparallel resonance unit 202 as illustrated in FIG. 4. For example,another configuration is also preferable in which the impedanceadjustment circuit 142 (143) is coupled to the negative side terminal(the node NDN) of the parallel resonance unit 202.

Embodiment 3

FIG. 5 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 3.

The electric power receiving device 2 according to Embodiment 1 performsthe linear control over the impedance adjustment circuit for adjustingthe resonance frequency of the resonance circuit, by means of thedifferential amplifier circuit; however, an electric power receivingdevice 5 according to Embodiment 3 performs the switching control overthe impedance adjustment circuit, by means of a comparator circuit.

As illustrated in FIG. 5, the electric power receiving device 5 in thenon-contact power supply system 22 is provided with a resonancefrequency adjustment unit 150 configured with a comparator circuit CMP,in lieu of the resonance frequency adjustment unit 140 according toEmbodiment 1. The resonance circuit 130B of the electric power receivingdevice 5 is provided with impedance adjustment circuits 147 and 148, inlieu of the impedance adjustment circuits 142 and 143 according toEmbodiment 1. The configuration of other parts of the electric powerreceiving device 5 is the same as that of the electric power receivingdevice 2 according to Embodiment 1, therefore, the same symbol isattached to the same component as the electric power receiving device 2,and the detailed explanation thereof is omitted.

The comparator circuit CMP compares the rectified voltage VRCT with thetarget voltage VTGT and outputs the comparison result. For example, thecomparator circuit CMP outputs a comparison result signal 149 of a highlevel (High), when the output voltage VRCT is greater than the targetvoltage VTGT, and outputs a comparison result signal 149 of a low level(Low), when the output voltage VRCT is smaller than the target voltageVTGT.

The impedance adjustment circuit 147 includes a capacitor CP of whichone end is coupled to the node NDP and a switching element SW1 providedbetween the other end of the capacitor CP and the ground node. Theswitching element SW1 is on-off controlled, on the basis of thecomparison result signal 149 from the comparator circuit CMP.

The impedance adjustment circuit 148 also has the same configuration asthe impedance adjustment circuit 147. For example, the impedanceadjustment circuit 148 includes a capacitor CN of which one end iscoupled to the node NDN and a switching element SW2 coupled between theother end of the capacitor CN and the ground node. The switching elementSW2 is the same as the switching element SW1.

In addition to a field effect transistor, an IGBT, etc. having a smallon-resistance and a high withstand voltage, mechanical switches, such asa relay switch, can be employed as the switching elements SW1 and SW2.When a mechanical switch is employed as the switching elements SW1 andSW2, parasitic capacitance of the switching elements SW1 and SW2 can bereduced. Therefore, it is possible to further alleviate the influence onthe resonance circuit according to the fact that the capacitors CP andCN are coupled to the nodes NDP and NDN, when the switching elements SW1and SW2 are set to OFF. Accordingly, it is possible to further reducethe setting error of the resonance frequency of the resonance circuit130 determined by the resonance coil 131 and the resonance capacitor132, at the time when the switching elements SW1 and SW2 are set to OFF.

In the present embodiment, as is the case with Embodiment 1, theconstants of the resonance coil 131 and the resonance capacitor 132 aredetermined so as to match the resonance frequency of the parallelresonance unit 202 with the electric power transmission frequency fTx.In this state, when the rectified voltage VRCT becomes lower than thetarget voltage VTGT, the comparison result signal 149 is set to, forexample, a low level by the comparator circuit CMP; accordingly, theswitching elements SW1 and SW2 are set to OFF. Accordingly, thecapacitors CP and CN are brought to a disconnected state, and theresonance capacitor 132 becomes dominant as the capacity component inthe resonance circuit 130B. As a result, the resonance frequency of theresonance circuit 130B approaches the resonance frequency determined bythe resonance coil 131 and the resonance capacitor 132 (nearly equal tothe electric power transmission frequency fTx). That is, when therectified voltage VRCT is lower than the target voltage VTGT, thecontrol is performed so as to match the resonance frequency of theresonance circuit 130B with the electric power transmission frequencyfTx.

When the rectified voltage VRCT becomes higher than the target voltageVTGT, on the other hand, the comparison result signal 149 is set to ahigh level by the comparator circuit CMP, and the switching elements SW1and SW2 are set to ON. Accordingly, the resonance frequency of theresonance circuit 130B is determined by the resonance coil 131, theresonance capacitor 132, and the capacitors CP and CN, and deviates fromthe electric power transmission frequency fTx. That is, when therectified voltage VRCT is higher than target voltage VTGT, the controlis performed so as to shift the resonance frequency of the resonancecircuit 130B away from the electric power transmission frequency fTx.

FIG. 6 illustrates characteristics of the reception electric power whenthe resonance frequency is changed in the electric power receivingdevice 5 according to Embodiment 3.

In the figure, the vertical axis expresses reception electric power andthe horizontal axis expresses frequency. A reference symbol 300illustrates the characteristics of the reception electric power when therectified voltage VRCT is smaller than the target voltage VTGT (when theswitching elements SW1 and SW2 are set to OFF). A reference symbol 301illustrates the characteristics of the reception electric power when therectified voltage VRCT is greater than the target voltage VTGT (when theswitching elements SW1 and SW2 are set to ON). The frequency at the peakvalue of the characteristics 300 and 301 is a resonance frequency of theresonance circuit 130B in each of the characteristics.

As understood from the characteristics 300, when the rectified voltageVRCT is smaller than the target voltage VTGT, the switching elements SW1and SW2 are set to OFF, and the resonance frequency of the resonancecircuit 130B substantially coincides with the electric powertransmission frequency fTx.

Accordingly, the reception electric power by means of the resonancecircuit 130B (the reception electric power at the frequency fTx) becomesmaximum. On the other hand, as understood from the characteristics 301,when the rectified voltage VRCT is greater than the target voltage VTGT,the switching elements SW1 and SW2 are set to ON, and the resonancefrequency of the characteristics 301 deviates from the electric powertransmission frequency fTx greatly. Accordingly, the reception electricpower via the resonance circuit 130B (the reception electric power atthe frequency fTx) falls greatly.

In this way, by on-off controlling the switching elements SW1 and SW2(by performing the switching control), depending on whether therectified voltage VRCT exceeds the target voltage VTGT, the resonancefrequency undergoes a binary switching control, and the electric powerreceiving device 6 shifts between the reception enabled state (thecharacteristics 300) and the reception disenabled state (thecharacteristics 301). Accordingly, when taking a time average, thereception electric power will settle in the desired electric power (themean electric power of the characteristics 300 and the characteristics301). Therefore, it is possible to restrict the reception electric powerof the electric power receiving device, and to suppress the heatgeneration of the electric power receiving device.

FIG. 5 illustrates the configuration in which the impedance adjustmentcircuits 147 and 148 are coupled to the terminals of both sides (thenodes NDP, NDN) of the parallel resonance unit 202, respectively.However, it is also preferable to employ the configuration in which animpedance adjustment circuit is coupled to either of the nodes NDP andNDN, such as the electric power receiving device 4 according toEmbodiment 2. According to this configuration, the symmetry of ACsignals corresponding to the reception electric power generated at thenode NDP and the node NDN may collapse. However, when the degree of thecollapse of the symmetry is allowable, it is possible to reduce thenumber of components which are otherwise to be added. Therefore, it ispossible to suppress the increase in cost of the electric powerreceiving device accompanied by enabling the adjustment of the resonancefrequency.

Embodiment 4

FIG. 7 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 4.

An electric power receiving device 6 in a non-contact power supplysystem 23 according to Embodiment 4 is different from the electric powerreceiving device 5 according to Embodiment 3 in the point that pluralcomparator circuits perform the switching control of plural impedanceadjustment circuits.

As illustrated in FIG. 7, the electric power receiving device 6 includesplural comparator circuits 150_1-150 _(—) n (n is an integer greaterthan one). The comparator circuits 150_1-150 _(—) n are supplied withrespectively different threshold voltages VTGT1-VTGTn. For example, whenthe target voltage of the rectified voltage VRCT is 10V, the thresholdvoltages VTGT1-VTGTn are set up as a gradually increasing voltage to thetarget voltage, such that the threshold voltage VTGT1 is 10V, thethreshold voltage VTGT2 is 11V, the VTGT3 is 12V, and so on.

A resonance circuit 130C includes n impedance adjustment circuits151_1-151 _(—) n, provided respectively corresponding to the comparatorcircuits 150_1-150 _(—) n. For example, the impedance adjustment circuit151_1 includes a capacitor CN_1 and a switching element SW_1. One end ofthe capacitor CN_1 is coupled to one terminal of the parallel resonanceunit 202 (the node NDP or the node NDN), and the switching element SW_1is coupled between the other end of the capacitor CN_1 and the referencenode (ground node). The impedance adjustment circuits 151_2-151 _(—) nhave the same configuration as the impedance adjustment circuit 151_1,and include capacitors CN_2-CN_n and switching elements SW_2-SW_n,respectively. FIG. 7 illustrates the case where one end of each of thecapacitors CN_1-CN_n is coupled to the node NDN; however, the one endmay be coupled to the node NDP. As the switching elements SW_1-SW_n, ahigh withstand voltage transistor, a mechanical switch, etc. may beemployed, as is the case with the switching element SW.

The impedance adjustment circuits 151_1-151 _(—) n are controlled by thecorresponding comparison result signals 149_1-149 _(—) n of thecomparator circuits 150_1-150 _(—) n. For example, in the impedanceadjustment circuit 151_1, the switching element SW_1 is on-offcontrolled by the comparison result signal 149_1 of the comparatorcircuit 150_1, and in the impedance adjustment circuit 151 _(—) n, theswitching element SW_n is on-off controlled by the comparison resultsignal 149 _(—) n of the comparator circuit 150 _(—) n.

Here, the constants of the resonance coil 131 and the resonancecapacitor 132 are determined so as to match the resonance frequency ofthe parallel resonance unit 202 with the electric power transmissionfrequency fTx when all the switching elements SW_1-SW_n of the impedanceadjustment circuits 151_1-151 _(—) n are set to OFF.

The following explains concretely the control of the reception electricpower by means of the electric power receiving device 6, for the case ofn=3 as the number of the comparator circuits and the impedanceadjustment circuits. It is assumed that VTGT1=10V, VTGT2=12V, andVTGT3=14V.

FIG. 8 illustrates characteristics of the reception electric power whenthe resonance frequency is changed in the electric power receivingdevice 6 according to Embodiment 4.

In the figure, the vertical axis expresses reception electric power andthe horizontal axis expresses frequency. The reference symbol 400illustrates the characteristics of the reception electric power when therectified voltage VRCT is smaller than the threshold voltage VTGT1(10V). The reference symbol 401 illustrates the characteristics of thereception electric power when the rectified voltage VRCT is greater thanthe threshold voltage VTGT1 (10V) and smaller than the threshold voltageVTGT2 (12V). The reference symbol 402 illustrates the characteristics ofthe reception electric power when the rectified voltage VRCT is greaterthan the threshold voltage VTGT2 (12V) and smaller than the thresholdvoltage VTGT3 (14V). The reference symbol 403 illustrates thecharacteristics of the reception electric power when the rectifiedvoltage VRCT is greater than the threshold voltage VTGT3 (14V).

As understood from the characteristics 400, when the rectified voltageVRCT is smaller than the threshold voltage VTGT1 (10V), all theswitching elements SW_1-SW_3 are set to OFF, and the resonance frequencyof the resonance circuit 130C substantially coincides with the electricpower transmission frequency fTx. Accordingly, the reception electricpower by means of the resonance circuit 130C becomes the maximum.

As understood from the characteristics 401, when the rectified voltageVRCT is greater than the threshold voltage VTGT1 (10V) and smaller thanthe threshold voltage VTGT2 (12V), only the switching element SW_1 isset to ON, and the resonance frequency of the characteristics 401departs from the electric power transmission frequency fTx. Accordingly,the reception electric power (the reception electric power at thefrequency fTx) by means of the resonance circuit 130C decreases ratherthan the case of the characteristics 400.

As understood from the characteristics 402, when the rectified voltageVRCT is greater than the threshold voltage VTGT2 (12V) and smaller thanthe threshold voltage VTGT3 (14V), the switching elements SW_1 and SW_2are set to ON, and the resonance frequency departs further from theelectric power transmission frequency fTx. Accordingly, the receptionelectric power by means of the resonance circuit 130C decreases furtherthan the case of the characteristics 401.

Furthermore, as understood from the characteristics 403, when therectified voltage VRCT is greater than the threshold voltage VTGT3(12V), all the switching elements SW_1-SW_3 are set to ON, and theresonance frequency departs further from the electric power transmissionfrequency fTx. Accordingly, the reception electric power by means of theresonance circuit 130C decreases further than the case of thecharacteristics 402.

In this way, by switching the impedance of the resonance circuit 130Cstepwise corresponding to the voltage level of the rectified voltageVRCT, it is possible to change the resonance frequency stepwise.Therefore, it is possible to perform the control of the reception statein a similar manner as the analog control (linear control). Accordingly,the electric power receiving device is stabilized with the electricpower reception characteristics corresponding to the necessary electricpower amount. Therefore, when there is no change in the transmissionelectric power and the power consumption of the electric power receivingdevice, no shift of the reception state will take place; accordingly,generation of the switching noise in the control system is suppressed.Therefore, it is possible to reduce the EMI noise, compared with thecontrol in which the state transition occurs between two states of thereception enabled state and the reception disenabled state.

Embodiment 5

FIG. 9 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 5.

An electric power receiving device 7 in a non-contact power supplysystem 24 according to Embodiment 5 is different from the electric powerreceiving device according to the other embodiments in the point that aPIN diode is used as the impedance adjustment circuit for adjusting theresonance frequency of the resonance circuit.

As illustrated in the figure, the electric power receiving device 7includes an impedance adjustment circuit 152. The impedance adjustmentcircuit 152 is configured with capacitors C4 and C5, a PIN diode DPN,resistors RP and RN, and a transistor M3, for example. The capacitor C4,the PIN diode DPN, and the capacitor C5 are coupled in series betweenthe node NDP and the node NDN. The anode of the PIN diode DPN is coupledto the node NDP via the capacitor C4, and the cathode is coupled to thenode NDN via the capacitor C5. The anode of the PIN diode DPN is coupledto a node VDD to which a bias voltage is supplied via the resistor RP(for example, a power node to which the power supply voltage issupplied). The cathode of the PIN diode DPN is coupled to the groundnode via the resistor RN and the transistor M3. A gate electrode of thetransistor M3 is driven by a control voltage 144 of the differentialamplifier circuit AMP. As the transistor M3, a field effect transistor,an IGBT, etc. having a small on-resistance and a high withstand voltagecan be employed. The configuration of other parts of the electric powerreceiving device 7 is the same as that of the electric power receivingdevice 2 according to Embodiment 1.

According to the above-described configuration, the transistor M3 iscontrolled by the differential amplifier circuit AMP; accordingly, thebias voltage applied to the PIN diode DPN is adjusted and thecapacitance value of the rectifier circuit 133 changes. Accordingly, theresonance frequency is adjusted so as to keep the rectified voltage VRCTfrom exceeding the target voltage VTGT. Therefore, it is possible torestrict the reception electric power of the electric power receivingdevice 7, and to suppress the heat generation of the electric powerreceiving device 7. It is possible to change easily the capacitancevalue of the resonance circuit by employing the PIN diode DPN.

Embodiment 6

FIG. 10 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 6.

An electric power receiving device 8 in a non-contact power supplysystem 25 according to Embodiment 6 is different from the electric powerreceiving device according to the other embodiments in the point thatthe inductance of the resonance coil 131 is changed in order to adjustthe resonance frequency of the resonance circuit.

The electric power receiving device 8 illustrated in the figure isprovided with switching elements 155 and 156 for adjusting theinductance of the resonance coil 131 in the resonance circuit 130E. Theswitching element 156 is coupled between an intermediate node ND1 of theresonance coil 131 and the node NDP, and the switching element 155 iscoupled between an intermediate node ND2 of the resonance coil 131 andthe node NDN. The switching elements 155 and 156 are on-off controlledby the comparison result signal 149 of the comparator circuit CMP. Theconfiguration of other parts in the electric power receiving device 8 isthe same as that of the electric power receiving device 5 according toEmbodiment 3.

The constants of the resonance coil 131 and the resonance capacitor 132have been determined so as to match the resonance frequency determinedby the resonance coil 131 and the resonance capacitor 132 with theelectric power transmission frequency fTx when the switching elements155 and 156 are set to OFF.

For example, when the rectified voltage VRCT is smaller than the targetvoltage VTGT, the switching elements 155 and 156 are set to OFF, and theinductance of the resonance coil 131 becomes the maximum; accordingly,the resonance frequency of the resonance circuit 130E substantiallycoincides with the electric power transmission frequency fTx.Accordingly, the reception electric power by means of the resonancecircuit 130E becomes the maximum. When the rectified voltage VRCT isgreater than the target voltage VTGT on the other hand, the switchingelements 155 and 156 are set to ON, and the inductance of the resonancecoil 131 decreases; accordingly, the resonance frequency of theresonance circuit 130E deviates from the electric power transmissionfrequency fTx. Accordingly, the reception electric power of theresonance circuit 130D decreases greatly.

As described above, the inductance of the resonance circuit 130E isadjusted, and the resonance frequency is adjusted so as to keep therectified voltage VRCT from exceeding the target voltage VTGT.Therefore, it is possible to restrict the reception electric power ofthe electric power receiving device 8, and to suppress the heatgeneration of the electric power receiving device 8.

Embodiment 7

FIG. 11 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 7.

An electric power receiving device 9 in a non-contact power supplysystem 26 according to Embodiment 7 is different from the electric powerreceiving device according to the other embodiments in the point thatthe reception electric power is monitored by monitoring the inputvoltage of the rectifier circuit 133.

The electric power receiving device 9 illustrated in the figure furtherincludes an input voltage detection unit 160 for detecting the inputvoltage supplied to the rectifier circuit 133 via the resonance circuit130. The input voltage detection unit 160 includes for example, a peakhold circuit (PH_CIRP) 162 which detects the peak value of the positiveside input voltage of the rectifier circuit 133 (voltage at the nodeNDP), and a peak hold circuit (PH_CIRN) which detects the peak value ofthe negative side input voltage of the rectifier circuit 133 (voltage atthe node NDN). The input voltage detection unit 160 further includes anaveraging circuit 163 which outputs an average value of the peak valuedetected by the peak hold circuit 161 and the peak value detected by thepeak hold circuit 162.

The differential amplifier circuit AMP generates an control voltage 144so as to reduce the difference between the target voltage VTGT and adetection voltage VPA corresponding to the average value of two peakvalues which have been generated by the averaging circuit 163. Theconfiguration of other parts including the resonance circuit 130 of theelectric power receiving device 9 is the same as that of the electricpower receiving device 2 according to Embodiment 1.

According to this configuration, as is the case with the electric powerreceiving device 2 according to Embodiment 1, the resonance frequency isadjusted so as to keep the reception electric power from exceeding thetarget electric power level. Therefore, it is possible to restrict thereception electric power of the electric power receiving device 9, andto suppress the heat generation of the electric power receiving device9. The reception electric power is detected in the earlier stage thanthe rectifier circuit 133; therefore, it is possible to improve theresponsiveness of the control system (the control system after thereception electric power is detected until the impedance of theresonance circuit 130 is adjusted). By adopting the configuration inwhich each peak voltage at the node NDP and the node NDN is detected, itis possible to suppress the degradation of the detection accuracy in theinput voltage detection unit 160, even when the waveform of the ACsignals corresponding to the reception electric power generated at thenode NDP and the node NDN is asymmetrical.

Embodiment 8

FIG. 12 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 8.

An electric power receiving device 10 in a non-contact power supplysystem 27 according to Embodiment 8 is different from the electric powerreceiving device 11 according to Embodiment 7 in the point that theinput voltage of one side of the rectifier circuit 133 is monitored toadjust the resonance frequency.

An input voltage detection unit 164 in the electric power receivingdevice 10 illustrated in the figure includes a peak hold circuit(PH_CIRP) 162 which detects a peak value of the input voltage on thepositive side or the negative side of the rectifier circuit 133 (voltageat the node NDP or at the node NDN), for example. FIG. 12 illustratesthe configuration in which the peak value at the node NDP is detected bythe peak hold circuit 162; however, it is also preferable to adopt aconfiguration in which the peak value at the node NDN is detected.

The differential amplifier circuit AMP generates a control voltage 144so as to reduce the difference of a detection voltage VPP correspondingto the peak value detected by the peak hold circuit 162 and the targetvoltage VTGT. The configuration of other parts including the resonancecircuit 130 is the same as that of the electric power receiving device 2according to Embodiment 1.

According to this configuration, as is the case with the electric powerreceiving device 9 according to Embodiment 7, the resonance frequency isadjusted so as to keep the reception electric power from exceeding thetarget electric power level. Therefore, it is possible to restrict thereception electric power of the electric power receiving device 10, andto suppress the heat generation of the electric power receiving device10. According to the electric power receiving device 10, when thedetection accuracy by means of the input voltage detection unit 164 isallowable, it is possible to reduce the number of components which areotherwise to be added. Therefore, it is possible to suppress theincrease in cost of the electric power receiving device accompanied byenabling the adjustment of the resonance frequency.

Embodiment 9

FIG. 13 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 9.

An electric power receiving device 11 in a non-contact power supplysystem 28 according to Embodiment 9 is different from the electric powerreceiving device according to the other embodiments in the point thatthe target voltage VTGT supplied to the resonance frequency adjustmentunit is variable.

As illustrated in FIG. 13, an electric power reception IC 170 in theelectric power receiving device 11 includes a voltage control unit 171in lieu of the power supply circuit 134. The voltage control unit 171inputs the rectified voltage VRCT and supplies the voltage to theinternal electronic circuit 139, the charging control circuit 135, etc.,as the load circuits which are coupled in the latter stage, and at thesame time, the voltage control unit 171 adjusts the target voltage VTGTso as to match the voltage to be supplied to the load circuits with thedesired voltage. The adjustment of the target voltage VTGT is realizedby, for example, controlling the above-described reference voltagegenerating circuit (not shown) provided in the electric power receivingdevice.

For example, when the voltage of 5V is to be supplied to the internalelectronic circuit 139, the charging control circuit 135, etc., thevoltage control unit 171 adjusts the target voltage VTGT so that theoutput voltage of the voltage control unit 171 may become 5V.Accordingly, assuming that the input-output voltage drop of the voltagecontrol unit 171 can be ignored, the reception electric power isrestricted so that the rectified voltage VRCT to be inputted to thevoltage control unit 171 may become 5V,

As described above, according to the electric power receiving device 11according to Embodiment 9, the output voltage of the rectifier circuit133 is adjusted, depending on the voltage level to be supplied to theload. Therefore, it is possible to generate a voltage necessary for theload, even if a DC-DC converter such as a regulator (the above-describedpower supply circuit 134, etc.) is not provided in the latter stage ofthe rectifier circuit 133. Therefore, if the requirement specificationof the electric power receiving device is satisfied, it is possible toremove the existing DC-DC converter etc., contributing to the reductionof the circuit scale of the electric power receiving device.

Embodiment 10

In the present embodiment, the electric power receiving device providedwith the function of controlling the reception electric power asillustrated in Embodiment 1 through Embodiment 9 is applied to anon-contact power supply system which is capable of performing wirelesscommunications other than the NFC communications. An example of theconfiguration of the present system is illustrated in FIG. 14.

FIG. 14 illustrates a non-contact power supply system including anelectric power receiving device according to Embodiment 10.

An electric power receiving device 12 in a non-contact power supplysystem 29 illustrated in the figure is different from the electric powerreceiving device according to the other embodiments in the point that acommunications antenna is provided separately from the resonance coil131 to perform wireless communications with the electric powertransmitting device.

In the non-contact power supply system 29, it is possible to performdata transmission/reception mutually between the electric powertransmitting device 3 and the electric power receiving device 12, by theshort distance radio communication. The short distance radiocommunication is wireless communications by a wireless LAN and Bluetooth(registered trademark), for example, using a frequency in GHz zone.

As illustrated in FIG. 14, the electric power transmitting device 3includes a communications antenna 111 in lieu of the above-describedcommunication coil antenna 106. The communication unit 105 performswireless communications with the electric power receiving device 12 viathe communications antenna 111. Other configurations are the same asthose of the electric power transmitting device 1 according toEmbodiment 1.

As illustrated in the figure, the electric power receiving device 12includes a communication unit (CMM_CIR) 181 and a communications antenna180 in lieu of the switching circuit 1370 and the communication controlcircuit 1371 described above. The communication unit 181 performswireless communications with the electric power transmitting devices 3via the communications antenna 180. Other configurations are the same asthose of the electric power transmitting device according to Embodiment1 through Embodiment 9. As the concrete configuration of the resonancefrequency adjustment unit 141 and the resonance circuit 130, it ispossible to apply various kinds of configurations illustrated inEmbodiment 1 through Embodiment 9 (the differential amplifier circuitAMP, the comparator circuit CMP, the resonance circuits 130A-130E,etc.).

According to this configuration, as is the case with Embodiment 1through Embodiment 9, it is possible not to receive an excessiveelectric power more than the electric power required by the electricpower receiving device, and to suppress the heat generation of theelectric power receiving device.

As described above, the invention accomplished by the present inventorshas been concretely explained based on the embodiments. However, itcannot be overemphasized that the present invention is not restricted tothe embodiments, and it can be changed variously in the range which doesnot deviate from the gist.

For example, in the configurations illustrated in Embodiment 1 throughEmbodiment 10, the output voltage VRCT or the input voltage (the voltageat the nodes NDP and NDN) of the rectifier circuit 133 is monitored.However, the configuration will not be restricted to the configurationillustrated above, as long as monitoring the reception electric power ispossible. For example, it is also preferable to monitor the receptionelectric power by monitoring the output current or input current of therectifier circuit 133, and to adjust the impedance of the resonancecircuit 130 on the basis of the monitored result. It is also possible toemploy a CM directional coupler, for example, as the detection circuitof the electric power amount.

The means for adjusting the resonance frequency of the resonance circuit130 is not restricted to the configuration illustrated in Embodiment 1through Embodiment 10; however, it is also possible to adopt variouscircuit configurations, as long as it is possible to change theresonance frequency of the resonance circuit 130.

The simple circuit configuration in which the resonant frequencyregulation circuit 141 is configured with the differential amplifiercircuit AMP or the comparator circuit CMP has been illustrated. However,the configuration will not be restricted to the one illustrated above,as long as it is possible to adjust the impedance of the resonancecircuit 130. For example, in order to improve the stability andreliability of the control, it is also possible to add a phasecompensation circuit to the differential amplifier circuit AMP, or toadd various logic circuits to the comparator circuit CMP.

In the electric power receiving device 6 according to Embodiment 4, itis also preferable to adopt the configuration in which, in addition tothe impedance adjustment circuits 151_1-151 _(—) n coupled to the nodeNDN, impedance adjustment circuits 151_1-151 _(—) n coupled to the nodeNDP are provided and on-off controlled by the corresponding comparatorcircuits. According to this configuration, as is the case with theelectric power receiving device 1 according to Embodiment 1, it ispossible to maintain the symmetry of the AC signals supplied to each ofthe node NDP and the node NDN.

In the electric power receiving device 7 according to Embodiment 5, theconfiguration in which the bias voltage of the PIN diode is controlledby means of the differential amplifier circuit AMP via the transistor M3has been illustrated. However, it is also possible to use the comparatorcircuit CMP in lieu of the differential amplifier circuit AMP. In thiscase, it is also preferable to adopt a configuration in which pluralcomparator circuits CMP and plural impedance adjustment circuits 152each including a PIN diode are provided and controlled as in theelectric power receiving device 6 according to Embodiment 4.

Embodiment 1 through Embodiment 10 have illustrated the case where thefunction for controlling the reception electric power is applied to theelectric power receiving device of the non-contact power supply systemof the magnetic resonance type. However, it is also possible to applythe function to an electric power receiving device in a non-contactpower supply system of the electromagnetic induction type. It is alsopossible to apply the function to a non-contact power supply systemwhich is configured with the electric power transmitting device and theelectric power receiving device, and which performs only the electricpower transmission and reception, without the communication function.According to this configuration, it is possible to reduce the size ofthe electric power transmitting device and the electric power receivingdevice, due to the deletion of a circuit, an antenna, etc. forcommunications, while enhancing the reliability of the non-contact powertransmission.

What is claimed is:
 1. An electric power receiving device comprising: aresonance circuit including a resonance capacitor and a resonance coilacting as a receiving antenna, the electric power receiving device beingoperable to receive electric power in a non-contact manner with the useof resonant coupling of the resonance circuit, wherein, in receiving theelectric power, the reception electric power received by the resonancecircuit is monitored, and a resonance frequency of the resonance circuitis controlled to keep the reception electric power from exceeding atarget electric power level.
 2. The electric power receiving deviceaccording to claim 1, wherein when the reception electric power is notexceeding the target electric power level, the impedance of theresonance circuit is adjusted so as to match the resonance frequency ofthe resonance circuit with an electric power transmission frequency, andwherein when the reception electric power is exceeding the targetelectric power level, the impedance of the resonance circuit is adjustedso as to shift the resonance frequency away from the electric powertransmission frequency.
 3. The electric power receiving device accordingto claim 2, further comprising: a rectifier circuit operable to rectifyan AC voltage corresponding to the electric power received by theresonance circuit to obtain a DC output voltage; and an adjustment unitoperable to monitor the output voltage of the rectifier circuit and toadjust impedance of the resonance circuit to keep the output voltagefrom exceeding a target voltage.
 4. The electric power receiving deviceaccording to claim 3, wherein the capacitance value of the resonancecircuit is changed by the adjustment unit.
 5. The electric powerreceiving device according to claim 4, wherein the adjustment unitcomprises: a differential amplifier circuit operable to generate acontrol voltage so as to reduce a difference of the target voltage andthe output voltage, wherein the resonance circuit comprises: a parallelresonance unit configured with the resonance coil and the resonancecapacitor coupled in parallel; and a first capacitor and a firstvariable resistance circuit coupled in series between one end of theparallel resonance unit and a reference node supplied with a fixedvoltage, and wherein the first variable resistance circuit changes avalue of resistance on the basis of the control voltage.
 6. The electricpower receiving device according to claim 5, wherein the resonancecircuit further comprises: a second capacitor and a second variableresistance circuit coupled in series between the other end of theparallel resonance unit and the reference node, and wherein the secondvariable resistance circuit changes a value of resistance on the basisof the control voltage.
 7. The electric power receiving device accordingto claim 6, wherein the first variable resistance circuit and the secondvariable resistance circuit respectively include a transistor driven bythe control voltage.
 8. The electric power receiving device according toclaim 4, wherein the adjustment unit comprises: a comparator circuitoperable to compare a threshold voltage corresponding to the targetvoltage with the output voltage, to output the comparison result, andwherein the resonance circuit comprises: a parallel resonance unitconfigured with the resonance coil and the resonance capacitor coupledin parallel; and a first capacitor and a first switching element coupledin series between one end of the parallel resonance unit and a referencenode supplied with a fixed voltage, and wherein the first switchingelement is on-off controlled, on the basis of the comparison result. 9.The electric power receiving device according to claim 8, wherein theresonance circuit further comprises: a second capacitor and a secondswitching element coupled in series between the other end of theparallel resonance unit and the reference node, and wherein the secondswitching element is on-off controlled on the basis of the comparisonresult.
 10. The electric power receiving device according to claim 9,wherein the constants of the receiving coil and the resonance capacitorof the parallel resonance unit are set up so as to match the resonancefrequency of the parallel resonance unit with the electric powertransmission frequency, when the first switching element and the secondswitching element are set to OFF, and wherein the adjustment unit setsthe first switching element and the second switching element to ON whenthe output voltage is exceeding the target voltage and sets the firstswitching element and the second switching element to OFF when theoutput voltage is not exceeding the target voltage.
 11. The electricpower receiving device according to claim 4, wherein the adjustment unitcomprises: a plurality of comparator circuits, each operable to comparea threshold voltage corresponding to the target voltage with the outputvoltage and to output the comparison result, wherein the resonancecircuit comprises: a parallel resonance unit configured with theresonance coil and the resonance capacitor coupled in parallel; and aplurality of impedance adjustment circuits, each including a firstcapacitor and a first switching element coupled in series between oneend of the parallel resonance unit and a reference node supplied with afixed voltage, wherein each of the comparator circuits has a mutuallydifferent threshold voltage, wherein the impedance adjustment circuitsare provided corresponding to the comparator circuits, and wherein thefirst switching element of each of the impedance adjustment circuits ison-off controlled, on the basis of the comparison result of thecorresponding comparator circuit.
 12. The electric power receivingdevice according to claim 10, wherein the first switching element andthe second switching element are mechanical switches which arecontrolled on the basis of the control voltage.
 13. The electric powerreceiving device according to claim 3, further comprising: a loadcircuit; and a voltage control unit operable to receive the outputvoltage of the rectifier circuit and to supply it to the load circuitcoupled in the latter stage, wherein the voltage control unit adjuststhe target voltage so as to match the voltage to be supplied to the loadcircuit with a desired voltage.
 14. The electric power receiving deviceaccording to claim 4, wherein the resonance circuit comprises a PINdiode to which a variable bias voltage is applied by the adjustmentunit.
 15. The electric power receiving device according to claim 3,wherein the resonance circuit changes the inductance of the receivingcoil.
 16. The electric power receiving device according to claim 3,further comprising: a rectifier circuit operable to rectify an ACvoltage corresponding to the electric power received by the resonancecircuit and to output a DC output voltage; an input voltage detectionunit operable to detect the input voltage supplied to the rectifiercircuit by the resonance circuit; and an adjustment unit operable toadjust the impedance of the resonance circuit to keep the input voltagedetected by the input voltage detection unit from exceeding a targetvoltage.
 17. The electric power receiving device according to claim 16,wherein the rectifier circuit is a full wave rectifier circuit, whereinthe input voltage detection unit comprises: a first peak hold circuitoperable to detect a peak value of a positive side input voltage of therectifier circuit; a second peak hold circuit operable to detect a peakvalue of a negative side input voltage of the rectifier circuit; and anaveraging circuit operable to output an average value of the peak valuedetected by the first peak hold circuit and the peak value detected bythe second peak hold circuit, and wherein the adjustment unit adjuststhe impedance of the resonance circuit to keep the average value of theaveraging circuit from exceeding the target voltage.
 18. A non-contactpower supply system comprising: an electric power transmitting deviceoperable to transmit electric power in a non-contact manner with the useof the electromagnetic resonant coupling utilizing the resonancecircuit; and the electric power receiving device according to claim 2,operable to receive the electric power transmitted by the electric powertransmitting device in a non-contact manner.
 19. An electric powerreceiving device comprising: a resonance circuit including a resonancecapacitor and a resonance coil acting as a receiving antenna, theelectric power receiving device being operable to receive the electricpower in a non-contact manner with the use of resonant coupling of theresonance circuit, wherein when receiving the electric power, theimpedance of the resonance circuit is dynamically controlled to matchthe reception electric power received by the resonance circuit with atarget electric power level.